Addition agent



Patented Oct. 24, 1933 UNITED STATES PATENT OFFICE ADDITION AGENT N 0 Drawing.

Serial No. 1932 Application December 3, 1928, 323,558. Renewed February 16,

4- Claims. (01. 294-1) This invention relates to a new and improved process for electrodepositing cadmium in a smooth, even layer from a cadmium containing solution.

In electrolytic processes in which cadmium is deposited on a cathode, a mist frequently rises from the electrolyte due to the bursting of bubbles, which are caused by the liberated gases. This may be suflicient to contaminate the atmosphere and render it difficult for operators to work in the tank house for any extended length of time. Furthermore, a deposit of cadmium obtained from a plain electrolyte such as cadmium sulphate and sulphuric acid, is frequently so irregular as to be unsuitable for certain commercial purposes.

The present invention is directed to a process which overcomes the above mentioned dificulties and includes means for preventing the formation of a mist above the electrolyte, and also for securing an even deposit of cadmium. The atmosphere above the electrolytic tanks is consequently kept free from impurities and does not cause discomfort to persons in the vicinity of the cells.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description in which a particular commercial embodiment thereof is disclosed. It will be understood, however, that the processes and the steps thereof may be modified in various respects without departing from the broad spirit and scope of the invention.

In the following description and in the claims the various steps in the process and the details comprising the invention will be identified by specific names for convenience but they are intended to be as generic in their application as the art will permit.

- The above objects and others which will be apparent to those skilled in the art are accom-- plished by adding certain materials to the electrolyte which serve to produce a foam on the surface thereof and at the same time to impart desirable characteristics to the cadmium deposit. The foam prevents bubbles from rising to the surface and bursting with the consequent formation of mist.

For the production of foam it is necessary to have present in the solution a colloid which can be adsorbed in the air bubbles and carried with them to the surface of the bath. The increased viscosity and decreased surface tension of the liquid film around the bubble, which are functions of the particular colloid employed, determine the stability of the foam.

Various foam producing colloids may be employed in' the present process, although it has been found thatdextrin-like materials or glucosides which are of colloidal dimensions are most suitable. Of these materials, saponin is-fo'und to have the most desirable foam producing properties and to give the greatest viscosity to the air bubbles. A suitable foam may be produced by the use of a comparatively small quantity of this substance.

More -specifically, this invention may be applied to the electroplating of cadmium from a solution of cadmium sulphate and sulphuric acid using inert anodes. The cadmium may be deposited as a coating over the surface of the cathode by the passage of anelectric current through the electrolyte in a well known manner.

In carrying on this process a small amount of a foam producing colloid such as saponin, as for example, 1 lb. for some 3000 gallons of electrolyte may be added to the electroplating cell. This substance may be added directly to the cell or may be mixed with the electrolyte before the same is introduced into the electrolytic tanks. It is preferably added in a dry condition, and if necessary may be stirred or otherwise thoroughly mixed with the electrolyte.

The above addition agents produce a foam on the surface of the cell and in the tanks through which the electrolyte is circulated. This foam is produced when the bubbles of gas given off on the anodes rise to the surface of the electrolyte or when a stream of the solution is poured into a tank. The particular quantity of foam is not important provided a sufiicient amount is formed to prevent gas bubbles from forcing their way therethrough. A foam. of substantially A in thickness has been found to be satisfactory for this purpose.

Obviously the exact amount of reagent added to produce this foam may be varied within comparatively wide limits. If an insufficient amount is employed the foam would not be sufiiciently thick to have the desired effect or might not cover the entire surface of the liquid, whereas if an excess of reagent is employed the cost of operation is correspondingly increased. The proportion given above is set forth by way of example and has been found satisfactory in commercial me.

In addition to the above mentioned property of causing a foam to be produced on the surface of the electrolyte, the reagents above mentioned cause the deposit of cadmium on the cathode to possess more desirable characteristics. A smooth,

dense deposit is obtained which is comparatively free from undesirable defects.

In addition to the agents mentioned above, the even deposition of cadmium may be assisted if desired, by the use of various other agents, as for example, caramel, shellac, casein or starch. While these later reagents in themselves do not assist in the production of the foam, they have the property of causing an even and smooth deposition of the cadmium on the cathode.

Various combinations of the above may be employed for the combined purpose of producing foam and securing an even deposit. It has been found that a mixture of saponin and starch is especially suited for this purpose. It is to be understood, however, that any of the colloidal foam producing agents may be incorporated with any addition agent capable of producing an even cathode deposit, in a percentage which may be determined by the particular requirements of the solution being treated.

Although certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be unwaists derstood that various omissions, substitutions and changes in the several steps of the process and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

l. The process of electroplating cadmium with insoluble anodes, which comprises passing a current through a cadmium sulphate electrolyte containing a small quantity of saponin.

2. An electrolyte for cadmium deposition with insoluble anodes comprising a cadmium sulphate solution, containing a small proportion of saponin.

3. In. the process of electroplating cadmium from a solution of cadmium sulphate in sulphuric acid, the step which comprises adding small quantities of a mixture of saponin and starch to the electrolyte and passing a current therethrough, whereby a foam is produced on the surface thereof and an even deposit of cadmium is secured.

4. An electrolyte for cadmium deposition comprising a solution of cadmium sulphate and sulphuric acid containing a small proportion of saponin and starch.

ROSCOE TEATS. RUDOLPH LEONARD HASCHE. 

